1. Field of the Invention
The present invention relates to a method for separating particles from liquid media. Specifically, the invention relates to separating microalgae or other small particles from liquid media using electro-flocculation, flotation, and physical separation of flocculated particles from the liquid media.
2. Description of Related Art
A major bottleneck for processing microalgae for use in bio-fuels, food supplements, and other products is separating the microalgae from the liquid growth medium. Two of the major methods currently used involve filtration or centrifugation. In the case of filtration, filters are frequently clogged by the microalgae. As a result, filter maintenance becomes costly and labor-intensive. Centrifugation, on the other hand, is very energy-intensive. Separating microalgae from liquid growth medium without the high costs of maintenance, labor, or energy would be highly beneficial. It would greatly raise the level of efficiency for harvesting microalgae. Thus, microalgae would become a more viable source of fuel as an alternative to fossil fuels. Additionally, such an invention may be useful in other applications, such as waste-water treatment. There are some prior art references that attempt to address these efficiency problems using a electro-flocculation and/or flotation, but they fall short of providing a system that provides an affordable, long term, commercially viable method of separating high concentrations of particles from a liquid media.
So as to reduce the complexity and length of the Detailed Specification, and to fully establish the state of the art in certain areas of technology, Applicant herein expressly incorporates by reference all of the following materials identified in each numbered paragraph below.
U.S. Pat. No. 6,663,766 to Adin et al. describes a water purification process for making potable water wherein impure water enters the bottom of a vessel and purified water exits the top of the vessel. U.S. Pat. No. 6,800,206 to Robinson describes using electro-flocculation for treating water in a reaction vessel where the pollutants are removed from the top of the reaction vessel. These inventions would be inadequate for large scale removal of flocculated particles because they are only intended to remove very low concentrations of pollutants from water and are not suitable for removing high concentrations of particles.
U.S. patent application Ser. No. 11/184,733 by Renaud describes a method for separating contaminants from an aqueous medium wherein the effluent, after being mixed with a flocculent, is allowed to settle in a vessel. The sludge that rises to the top is then removed by a device using a vacuum. This application teaches using a vacuum system for harvesting. Such construction, while perhaps useful in some situations, is not necessary for efficient harvesting and therefore unnecessarily increases the complexity of the device. Furthermore, this application erroneously overlooks the complexity and potential for improvement in the processes of electrocoagulation and electroflocculation. In reality, the complex vacuum separation column taught by this application would not be necessary if the electrocoagulation and electroflocculation step were carried out in a more efficient manner.
U.S. Pat. No. 4,101,409 to Austin describes an apparatus for treating sludge involving adding the sludge to a vessel, applying a current to metal plates in a vessel, and supplying pressurized air to the vessel in order to help the sludge float to the top. Austin also describes using a mechanized paddle system on a conveyor belt to remove the sludge that has floated to the top of the vessel. This invention incorporates the flocculation and separation into one vessel, which increases the complexity and reduces efficiency since the two actions are mutually inhibitive, i.e., flocculation is improved by increasing agitation while separation is improved by minimizing agitation.
U.S. Pat. No. 6,524,486 to Borodyanski et al. describes using a telescopic froth-flotation column for separating microalgae from a liquid suspension. A flocculating agent is added to the suspension and the suspension is added to the column as air bubbles are forced up the column. This invention describes using a chemical flocculating agent (like starch, ferric chloride, aluminum sulphate, or ketosones at a rate of 100-300 grams per ton of algae). This invention is not conducive to using electro-flocculation. Therefore, for the water to be recycled through the system, it must be subjected to a costly treatment. Alternatively, fresh water could be introduced for each batch of microalgae, but that is an economically inefficient use of water.
Applicant believes that the material incorporated above is “non-essential” in accordance with 37 CFR 1.57, because it is referred to for purposes of indicating the background of the invention or illustrating the state of the art. However, if the Examiner believes that any of the above-incorporated material constitutes “essential material” within the meaning of 37 CFR 1.57(c)(1)-(3), applicant will amend the specification to expressly recite the essential material that is incorporated by reference as allowed by the applicable rules.